Injection molding machine with offset moving platen actuator

ABSTRACT

An injection molding machine comprises a first platen and a second platen, the first platen movable relative to the second platen in an axial direction between open and closed positions, and a plurality of tie bars extending generally between the first and second platens for coupling together the first and second platens. At least a first locking device is mounted to the first platen and associated with a first one of the tie bars for selectively locking and unlocking the moving platen relative to the tie bar. At least a first clamping mechanism is mounted to the second platen and associated with the first tie bar, the clamping mechanism including clamp and unclamp chambers on either side of a piston for moving the piston towards clamp and unclamp positions to exert a clamping force and a mold break force, respectively. The machine further includes a traverse actuator comprising one or more linear actuators coupled to at least one of the first and second platens for effecting said movement of the first platen relative to the second platen between the open and closed positions, the one or more linear actuators together being free of provision for applying a mold break force to the platens.

This application is a continuation of PCT Patent Application No.PCT/CA2009/001398, filed on Oct. 2, 2009, which claims priority fromU.S. Provisional Patent Application No. 61/102,633, filed on Oct. 3,2008, each of which is incorporated herein by reference in its entirety.

FIELD

The specification relates to injection molding machines, elementsthereof, and methods and apparatuses for controlling motion of molds inan injection molding machine.

BACKGROUND

U.S. Pat. No. 2,976,569 (Quere et al.) discloses a material formingapparatus comprising mould sections adapted to be slidably displacedwith respect to each other, a hydraulic pressure mechanism including aplurality of pressure cylinders, said pressure mechanism being adaptedto draw the mould sections together under high pressure, releasablecoupling rods and intermediate coupling means adapted to effect aselective coupling between the pressure cylinders and one of the mouldsections, a driving mechanism working independently of the pressurecylinders and adapted to drive said rods and intermediate coupling meansso that a selective coupling can be effected in unloaded condition ofthe coupling means, said coupling means including a plurality of clawson each coupling rod, and coupling sleeves carried by the other of saidmould sections and internally including claws for engaging the firstsaid claws, the coupling sleeves and the coupling rods being adapted forrotation with respect to each other by means of said driving mechanism,each pressure cylinder of the pressure mechanism being arranged adjacentthe associated coupling means which are rotatable in the driving means.

U.S. Pat. No. 5,620,723 (Glaesener et al.) discloses an injectionmolding machine that includes a stationary platen including at least onestationary mold half and a first movable platen. The first movableplaten is movable relative the stationary platen and has a second moldhalf adapted to engage the stationary mold half to form a first mold. Asecond movable platen may also be provided which is movable toward thestationary platen and includes a third mold half adapted to engage afourth mold half included with one of the stationary platen and thefirst movable platen. The third and fourth mold halves form a secondmold. Each of the first and second molds having a hot runner leadingthereto and an injection unit is provided for delivering melt to the hotrunners of the first and second molds. The machine further includes tiebars extending between and connecting the stationary platen and themovable platens. At least one of the first and, if used, the secondmovable platen and stationary platen includes a mechanism for securingat least one of the tie bars. The mechanism for securing comprises anengagement mechanism for placing the mechanism for securing into and outof locking engagement with at least one of the tie bars such that whenthe engagement mechanism is out of locking engagement with the at leastone tie bar, the mechanism for securing and the at least one tie bar arerelatively movable

U.S. Pat. No. 5,753,153 (Choi) discloses a system and process forcontrolling mold activity of a molding machine that includes a clampingdevice for positioning a movable mold platen on a carrier device andrelative another platen, for forcefully engaging the movable mold platenwith the another platen and on the carrier device, for sustainingforceful engagement of the movable mold platen with the another platenand the carrier device, and for breaking the movable platen from theanother platen and the carrying device. The movable mold platen includesa movable mold half and the another platen includes another mold half.The system also includes a manner for determining an adjustable startingposition of the clamping device and movable mold platen. A manner foradjusting the adjustable starting position for achieving greateraccuracy of the adjustable starting position for the clamping device andthe movable platen is provided. The manner for adjusting includes amechanism for actuating the clamping device. A device for monitoring andcontrolling the position of the clamping device and movable platen isprovided as well as a mechanism for sustaining the clamp-up force at aprescribed level.

U.S. Pat. No. 7,404,920 (Nogueira) discloses a molding-system clampassembly of a molding system, which includes a clamp piston, and a clampram, the clamp ram and the clamp piston each including inter-meshablestructures to selectively inter-mesh the clamp piston to the clamp ram.In the unmeshed position the clamp piston and the clamp ram do notinter-mesh relative to each other. The assembly includes inter-abuttablestructures to selectively inter-abut the clamp piston relative to theclams ram, the inter-abuttable structures having an interposing bodyabuttable against the clamp ram and the clamp piston, theinter-abuttable structures to abut with each other so that the clamppiston makes contact with the interposing body. The inter-abuttablestructures are configured to transfer a mold-break force so that themold-break force is applied from the clamp piston against theinterposing body, and in response the mold-break force is transferredfrom the clamp piston through the interposing body and to the clamp ram,and once mold break has occurred, the clamp piston is deactivated sothat the mold may be opened.

U.S. Published Pat. Appn. 2008/0187771 (Schad et al.) discloses (i) aclamp of a molding system, (ii) a molding system having a clamp, (iii) amethod of a clamp of a molding system, (iv) a molded articlemanufactured by usage of a clamp of a molding system, (v) a moldedarticle manufactured by usage of a molding system including a clamp, and(vi) a molded article manufactured by usage of a method of a clamp of amolding system. A disclosed embodiment of a clamp assembly includes apressure chamber for moving a piston to exert a clamping force on amold, and a spring acting on a rest plate in a direction opposite theclamping force to position the piston in a home position when the forceexerted by pressurized fluid in the clamping chamber is less than thespring force.

SUMMARY

The following summary is intended to introduce the reader to variousaspects of the applicant's teaching, but not to define any invention. Ingeneral, disclosed herein are one or more methods or apparatuses relatedto injection molding, and to positioning, locking, and clamping molds ininjection molding machines.

According to some aspects, an injection molding machine comprises: a) afirst platen and a second platen, the first platen movable relative tothe second platen in an axial direction between open and closedpositions; b) a plurality of tie bars extending generally between thefirst and second platens for coupling together the first and secondplatens; c) at least a first locking device mounted to the first platenand associated with a first one of the tie bars, the first lockingdevice and first tie bar comprising respective locking elements moveablefrom an unlocked position to a locked position when the tie bar is movedaxially relative to the locking device to one of a plurality of axiallyspaced apart meshing positions, the first locking device lockingtogether the first tie bar and the first platen when in the lockedposition, and the first locking device moveable from the locked positionto the unlocked position to release the first platen from the first tiebar; d) at least a first clamping mechanism mounted to the second platenand associated with the first tie bar, the first clamping mechanismcomprising a piston member affixed to the first tie bar and movablebetween clamp and unclamp positions within a cylinder housing affixed tothe second platen, the piston and cylinder housing defining a clampchamber and an unclamp chamber on opposite sides of the piston, formoving the piston towards the clamp and unclamp positions and exerting aclamping force and a mold break force, respectively, when pressurized,the clamping force being less than or equal to a maximum rated loadassociated with the machine; and e) a traverse actuator comprising oneor more linear actuators coupled to at least one of the first and secondplatens for effecting said movement of the first platen relative to thesecond platen between the open and closed positions, the one or morelinear actuators together being free of provision for applying a moldbreak force to the platens.

In some examples of such a machine, the one or more linear actuators ofthe traverse actuator together apply a net axial opening force on the atleast one platen in a direction opposite the clamping force and at avertical and/or horizontal location that is substantially offset fromthe center of the at least one platen as viewed in a plane orthogonal tothe axial direction. The one or more linear actuators of the traverseactuator together can be sized to exert a maximum opening force on theat least one platen in a direction opposite the clamping force that isless than about 3% of the maximum rated load.

In some examples, the injection molding machine can further comprise apositioning member movable relative to the piston and the cylinderhousing and moveable between an advanced position and a retractedposition, the positioning member when in the advanced position providinga mechanical stop for the piston when the piston is moved to a datumposition intermediate the clamp and unclamp positions. The positioningmember can be releasably retainable in the advanced position. Whenretained in the advanced position, the positioning member can interferewith sliding of the piston within the cylinder housing when moving fromthe clamp position in at least one direction, for example, from theclamp position towards the unclamp position. When the positioning memberis released from the advanced position and displaced towards theretracted position, the positioning member can be free of interferingwith the piston when the piston slides from the clamped position towardsthe unclamped position.

In some examples, the clamp chamber is be disposed on a clamp side ofthe piston, and the positioning member is disposed in the cylinderhousing on the clamp side of the piston. The positioning member cancomprise an annular sleeve coupled to the piston and axiallydisplaceable relative to the piston. An inner surface of the annularsleeve can slide along an outer surface of the piston. A pushing membercan be provided adjacent the annular sleeve to move the annular sleeveto the advanced position. The pushing member can comprises a positioningchamber disposed between the piston and the positioning member, thepositioning chamber urging the annular sleeve to the advanced positionwhen pressurized. In some examples, the pushing member can comprise oneor a plurality of springs, for example, compressions springs, and thesprings can be preloaded to provide a positioning force (urging thepositioning member to the advanced position) that is greater than adatum force (urging the piston to the datum position).

The traverse actuator may comprise a motor. The motor may be mountedbeneath at least one of the first platen and the second platen. Themotor may be axially aligned with one of the first platen and the secondplaten. Alternately, the motor may be axially inboard of one of thefirst platen and the second platen.

According to another aspect, an injection molding machine is provided.The injection molding machine comprises: a) a first platen and a secondplaten, the first platen movable relative to the second platen in anaxial direction between open and closed positions; b) a plurality of tiebars extending generally between the first and second platens forcoupling together the first and second platens; c) at least a firstlocking device mounted to the first platen and associated with a firstone of the tie bars, the first locking device and first tie barcomprising respective locking elements moveable from an unlockedposition to a locked position when the tie bar is moved axially relativeto the locking device to one of a plurality of axially spaced apartmeshing positions, the first locking device locking together the firsttie bar and the first platen when in the locked position, and the firstlocking device moveable from the locked position to the unlockedposition to release the first platen from the first tie bar; and d) atleast a first clamping mechanism mounted to the second platen andassociated with the first tie bar, the first clamping mechanismcomprising a piston member affixed to the first tie bar and movablebetween clamp and unclamp positions within a cylinder housing affixed tothe second platen, the piston and cylinder housing defining a clampchamber and an unclamp chamber on opposite sides of the piston, formoving the piston towards the clamp and unclamp positions and exerting aclamping force and a mold break force, respectively, when pressurized,the clamping force being less than or equal to a maximum rated loadassociated with the machine; and d) a traverse actuator comprising oneor more linear actuators coupled to at least one of the first and secondplatens for effecting said movement of the first platen relative to thesecond platen between the open and closed positions, wherein the one ormore linear actuators of the traverse actuator together apply a netaxial opening force on the at least one platen in a direction oppositethe clamping force and at a vertical and/or horizontal location that issubstantially offset from the center of the at least one platen asviewed in a plane orthogonal to the axial direction.

The one or more linear actuators of the traverse actuator together maybe sized to exert a maximum opening force on the at least one platen ina direction opposite the clamping force that is less than about 3% ofthe maximum rated load.

The traverse actuator may comprise a motor, and the motor may be mountedbeneath at least one of the first platen and the second platen. Themotor may be axially aligned with one of the first platen and the secondplaten. Alternately, the motor may be axially inboard of one of thefirst platen and the second platen.

According to another aspect, an injection molding machine comprises: a)a first platen and a second platen, the first platen movable relative tothe second platen in an axial direction between open and closedpositions; b) a plurality of tie bars extending generally between thefirst and second platens for coupling together the first and secondplatens; c) at least a first locking device mounted to the first platenand associated with a first one of the tie bars, the first lockingdevice and first tie bar comprising respective locking elements moveablefrom an unlocked position to a locked position when the tie bar is movedaxially relative to the locking device to one of a plurality of axiallyspaced apart meshing positions, the first locking device lockingtogether the first tie bar and the first platen when in the lockedposition, and the first locking device moveable from the locked positionto the unlocked position to release the first platen from the first tiebar; d) at least a first clamping mechanism mounted to the second platenand associated with the first tie bar, the first clamping mechanismcomprising a piston member affixed to the first tie bar and movablebetween clamp and unclamp positions within a cylinder housing affixed tothe second platen, the piston and cylinder housing defining a clampchamber and an unclamp chamber on opposite sides of the piston, formoving the piston towards the clamp and unclamp positions and exerting aclamping force and a mold break force, respectively, when pressurized,the clamping force being less than or equal to a maximum rated loadassociated with the machine; and e) a traverse actuator comprising oneor more linear actuators coupled to at least one of the first and secondplatens for effecting said movement of the first platen relative to thesecond platen between the open and closed positions, the one or morelinear actuators together being free of provision for applying a moldbreak force to the platens.

In some examples, the one or more linear actuators of the traverseactuator together apply a net axial opening force on the at least oneplaten in a direction opposite the clamping force and at a verticaland/or horizontal location that is substantially offset from the centerof the at least one platen as viewed in a plane orthogonal to the axialdirection. The one or more linear actuators of the traverse actuatortogether can be sized to exert a maximum opening force on the at leastone platen in a direction opposite the clamping force that is less thanabout 3 percent of the maximum rated load. The machine can furthercomprise a stop member movable relative to the piston and the cylinderhousing and moveable between an advanced position and a retractedposition, the stop member when in the advanced position providing amechanical stop for the piston when the piston is moved to a datumposition intermediate the clamp and unclamp positions.

The traverse actuator can comprise a motor, and the motor can be mountedbeneath at least one of the first platen and the second platen.Alternately, the motor can be positioned at an axial position generallyequal to that of one of the first platen and the second platen, or themotor can be axially inboard of one of the first platen and the secondplaten.

In some examples, the traverse actuator comprises a ball screw coupledto the motor and a ball nut fixed to the other of the first and secondplatens and in engagement with the ball screw. In some examples, thetraverse actuator comprises a toothed belt driven by the motor andaffixed to the other of the first and second platens.

The injection molding machine can further comprise four tie barsextending between respective corners of the first and second platens,and the traverse actuator can be positioned outside of a space boundedby the tie bars. One of the first and second platens can be a stationaryplaten remaining in a fixed axial position during use, and the singlelinear actuator can have a proximate end axially positioned generally atthe fixed axial position of the stationary platen.

According to some aspects, an injection molding machine comprises: a) afirst platen and a second platen, the first platen movable relative tothe second platen in an axial direction between open and closedpositions; b) a sprue bushing mounted in one of the first and secondplatens generally at a geometrically central position thereof, the spruebushing receiving melt from an injection nozzle therethrough, themachine having a machine axis parallel to the axial direction andpassing through the sprue bushing; c) a plurality of tie bars extendinggenerally between the first and second platens for coupling together thefirst and second platens; d) at least a first locking device mounted tothe first platen and associated with a first one of the tie bars, thefirst locking device and first tie bar comprising respective lockingelements moveable from an unlocked position to a locked position whenthe tie bar is moved axially relative to the locking device to one of aplurality of axially spaced apart meshing positions, the first lockingdevice locking together the first tie bar and the first platen when inthe locked position, and the first locking device moveable from thelocked position to the unlocked position to release the first platenfrom the first tie bar; e) at least a first clamping mechanism mountedto the second platen and associated with the first tie bar, the firstclamping mechanism comprising a piston member affixed to the first tiebar and movable between clamp and unclamp positions within a cylinderhousing affixed to the second platen, the piston and cylinder housingdefining a clamp chamber and an unclamp chamber on opposite sides of thepiston, for moving the piston towards the clamp and unclamp positionsand exerting a clamping force and a mold break force, respectively, whenpressurized, the clamping force being less than or equal to a maximumrated load associated with the machine; and f) a traverse actuatorcomprising a single linear actuator coupled to at least one of the firstand second platens for effecting said movement of the first platenrelative to the second platen between the open and closed positions,wherein the single linear actuator of the traverse actuator extendsalong an actuator axis that is generally parallel to the machine axisand offset in at least one of a horizontal and vertical direction fromthe machine axis.

The single linear actuator can be sized to exert a maximum opening forceon the at least one platen in a direction opposite the clamping forcethat is less than about 3 percent of the maximum rated load. Theinjection molding machine can comprise four tie bars extending betweenrespective corners of the first and second platens, and the singlelinear actuator can be positioned outside of a space bounded by the tiebars. One of the first and second platens can be a stationary platenremaining in a fixed axial position during use, and the single linearactuator can have a proximate end axially positioned generally at thefixed axial position of the stationary platen. The traverse actuator cancomprise a motor coupled to the single linear actuator, and the motorcan be mounted beneath at least one of the first platen and the secondplaten. Alternately, the motor can be positioned axially between, andlaterally aside, the first platen and the second platen.

Other aspects and features of the present specification will becomeapparent, to those ordinarily skilled in the art, upon review of thefollowing description of the specific examples of the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings included herewith are for illustrating various examples ofarticles, methods, and apparatuses of the present specification and arenot intended to limit the scope of what is taught in any way. In thedrawings:

FIG. 1 a is a schematic elevation view of a portion of an injectionmolding machine showing mold halves spaced apart by a positioning gap;

FIG. 1 b shows the machine of FIG. 1 a with the positioning gap closed;

FIG. 1 c shows the machine of FIG. 1 b with a clamping force exertedacross the mold halves;

FIG. 2 is an elevation view of an injection molding machine according tosome aspects of the Applicant's teaching;

FIG. 3 is an end view of an upper portion of the machine of FIG. 1;

FIG. 4 is a cross-sectional view of a portion of the machine of FIG. 3,taken along the lines 4-4;

FIG. 5 is an enlarged view of a first portion of the structure shown inFIG. 4;

FIG. 6 is a perspective view of the structure of FIG. 4, shown in anunlocked position;

FIG. 7 is an enlarged view of a second portion of the structure shown inFIG. 4;

FIG. 8 is an exploded view of the structure of FIG. 7;

FIGS. 9, 10, and 11 show the clamping device of FIG. 7 in a clamped,unclamped, and datum position, respectively;

FIG. 12 is a cross-sectional view similar to that of FIG. 7 showing analternate embodiment of a clamp mechanism;

FIG. 13 is a perspective view showing further details of the movingplaten traverse actuator of the injection molding machine of FIG. 2;

FIG. 14 is a cross section taken along line 14-14 in FIG. 13;

FIG. 15 is a perspective illustration of another example of a traverseactuator for a moving platen; and

FIG. 16 is a perspective illustration of another example of a traverseactuator for a moving platen.

DETAILED DESCRIPTION

Various apparatuses or processes will be described below to provide anexample of an embodiment of each claimed invention. No embodimentdescribed below limits any claimed invention and any claimed inventionmay cover processes or apparatuses that are not described below. Theclaimed inventions are not limited to apparatuses or processes havingall of the features of any one apparatus or process described below orto features common to multiple or all of the apparatuses describedbelow. It is possible that an apparatus or process described below isnot an embodiment of any claimed invention. Any invention disclosed inan apparatus or process described below that is not claimed in thisdocument may be the subject matter of another protective instrument, forexample, a continuing patent application, and the applicants, inventorsor owners do not intend to abandon, disclaim or dedicate to the publicany such invention by its disclosure in this document.

Referring first to FIG. 1 a, an injection molding machine 10 is shownhaving a base 12 upon which first and second platens 14, 16 are mounted.In the example illustrated, the injection molding machine 10 is atwo-platen type injection molding machine. The first platen 14 can slidein an axial direction along the base 12, towards and away from thesecond platen 16 which is stationary in the example illustrated. Atraverse actuator 24 can be provided to facilitate moving the movingplaten 14 between open and closed positions relative to the stationaryplaten 16. The platens 14, 16 support respective mold portions 14 a, 16a (also referred to as mold halves 14 a, 16 a). Tie bars 20 extendaxially between the platens for clamping the platens together duringoperation of the machine. A locking device 26 is, in the exampleillustrated, affixed to the moving platen 14 for releasably locking themoving platen 14 to a respective one of the tie bars 20. Clampingmechanisms 36 can be provided for exerting a clamping force across themold halves 14 a, 16 a during an injection cycle. In the exampleillustrated, the clamping mechanisms 36 include a cylinder housing 38affixed to the stationary platen 16, and a piston 40 affixed to arespective tie bar and slidable within the cylinder housing 38.

In use of the apparatus 10, the traverse actuator 24 can be energized toadvance the moving platen 14 towards a closed position relative to thestationary platen 16. The clamp piston 40 can be moved to a knownposition, for example, a fully unclamped position as shown in FIG. 1 a.The locking device 26 can be moved to the locked position to lock themoving platen 14 to a respective tie bar 20.

Prior to pressurizing the clamp chamber 60 of the clamping mechanism 36,the clamp piston 40 can be pre-positioned within the cylinder housing 38to a datum position that is axially intermediate the clamping positionand the unclamped position (FIG. 1 b).

Once the locking devices 26 have been moved to the locked position, theclamp chamber 60 can be pressurized so as to exert a clamping forceurging the mold halves 14 a, 16 a together. The piston 40 would be urgedfurther in the clamping direction (i.e. further to the right as shown inFIG. 1 c), stretching the tie bars 20 (within their elastic deformationlimit) and pulling the mold halves 14 a, 16 b tightly together. At anappropriate clamping force, the resin (or melt) can be injected into themold.

After the molded article has hardened sufficiently to allow ejection,the pressure in the clamp chamber 60 can be relieved. The unclampchamber 62 can be pressurized so as to exert a mold break force urgingthe mold halves 14 a, 16 a apart and moving the piston 40 to theunclamped position (as shown, for example, in FIG. 1 a). The mold breakforce exerted by the pressure in the unclamp chamber can be, forexample, from about 5 percent to about 10 percent (or more) of theclamping force. Such a mold break force may be required only in certaincases in which factors such as the geometry of the article to be molded,the material, and or specific process factors cause, for example, asubstantial residual clamping force to remain across the platens evenafter pressure in the clamp chamber has been relieved. In such cases,pressurizing the unclamp chamber can provide the necessary mold breakforce to urge the mold portions apart. In other cases, such a mold breakforce may not be requires, so that pressurizing the unclamp chamber(prior to shuttling the moving platen to the open position) may not benecessary.

Once pressure in the clamp chamber has been relieved (and after theoptional mold break force has been applied, if desired), the lockingdevices 26 can be moved to the unlocked position so as to unlock themoving platen 14 from the tie bars 20. The traverse actuator 24 can thenbe energized to retract the moving platen 14 to an open position spacedaway from the stationary platen 16. An ejection mechanism 25 can beenergized to facilitate ejecting the molded article from the mold.

Pre-positioning the piston 40 to a datum position intermediate the clampand unclamp positions can facilitate breaking open the mold after aninjection cycle, by ensuring that the piston 40 has room to travel backtowards the unclamped position after having been moved towards theclamping position. In some cases, the axial travel of the piston 40 inthe clamping direction can be minimal (particularly where the machinehas been tuned for maximum speed i.e. minimum cycle time). Additionallyor alternatively, in some cases the mold can flash (resin squeezing outbetween the mold halves 14 a, 16 a) during injection, which can push theclamp piston 40 back towards the unclamp position (clamping force—andtie bar stretch—can remain generally unchanged during mold flash, butthe piston can be displaced within the cylinder housing in response todisplacement of the moving platen 14 as a result of the resin forcingits way out between the mold halves). This could, in cases wherepre-positioning is not provided or not satisfactorily provided, causethe piston to bottom out in the cylinder in the unclamp direction (i.e.piston bears against back wall or other structural element thatphysically inhibits further travel of the piston in the unclampdirection).

If such bottoming out occurs while the tie bars are still loaded (i.e.bottoming out resulting from mold flash), then moving the lockingdevices 26 to the unlocked position can be very difficult or impossible.Destructive methods may then be required to open the mold and reset themachine for a new injection cycle. The teaching of the present inventioncan avoid this and/or other possible drawbacks by pre-positioning thepiston 40 at an intermediate position within its range of travel in thehousing 38 prior to clamping the mold halves together, so that ampletravel in the unclamp direction is available after an injection cycle,even in cases where the mold may flash, and also providing sufficientforward travel in the clamping direction for applying a desired clampingforce.

In some examples, the maximum stroke length of the piston in thecylinder housing can be in the range of about 15 to about 20 mm. Thedatum position of the piston can correspond to a position of about 6 mmto about 10 mm forward (in the clamp direction) of the fully back(unclamped) position, leaving, in the example illustrated, at leastabout 5 mm backward travel of the piston available for mold break. About10 mm forward travel of the piston can be provided for clamping the moldhalves together.

A variety of methods in accordance with the present teaching can beemployed to accomplish the pre-positioning of the piston 40. In oneexample, when moving the platen 14 from an open position towards theclosed position, the platen 14 can stop short of the stationary platen16 so as to leave a positioning gap 77 between the mold portion 14 a(secured to moving platen 14) and the mold portion 16 a (secured tostationary platen 16) (see FIG. 1 a). With the mold portions spacedapart by the positioning gap 77, the locking devices can be moved to thelocked position to secure together the moving platen 14 and the tie bars20. The traverse actuator can then be energized to further advance themoving platen 14 to substantially close the positioning gap 77. Duringclosing of the gap 77, the tie bars 20 are also advanced by the sameamount as the platen 14, since the moving platen 14 and tie bars 20 arelocked together. This moves the piston 40 from, for example, theunclamped position (FIG. 1 a) to the datum position (FIG. 1 b).

In some examples, when the mold portions 14 a, 16 a secured to themoving platen 14 and the stationary platen 16 are spaced apart by thepositioning gap 77, and the moving platen 14 is locked to the tie bars20, the clamp chamber 60 can be pressurized to urge the piston 40 (andtie bar 20) towards the clamping direction. This carries the movingplaten 14 along to close the positioning gap 77. The pressure in theclamping chamber during closing the gap 77 can be lower than thepressure in the clamping chamber during injection of the resin. Thetraverse actuator 24 can be energized to work in cooperation with theclamp piston 40, or can, for example, be placed in neutral mode so asnot interfere with, or be damaged by, the force exerted by the piston 40during closing of the positioning gap 77.

In some examples, moving the clamp piston 40 to the datum position caninclude moving a stop member to an advanced position relative to theclamp piston 40 and cylinder housing 38, and urging the clamp piston 40to bear against the stop member. An example of such a stop member isdescribed subsequently herein, for example, at positioning member 182 inthe apparatus 110. In the examples including a stop member, moving theclamp piston to the datum position can include pressurizing the unclampchamber, and venting the clamp chamber to tank. Furthermore, apositioning chamber in communication with the stop member can bepressurized for urging the stop member to the advanced position. Thestop member can be movably disposed between the clamp chamber and thepiston, such that moving the stop member from the retracted to theadvanced positions reduces the volume of the clamp chamber. In theseexamples, when advancing the moving platen from the open positiontowards the stationary platen, the traverse actuator can bring the moldportion 14 a (of the moving platen 14) almost right up against the moldportion 16 a (of the stationary platen 16) (i.e. no or zero positioninggap 77) prior to locking the moving platen to the tie bars. In theexamples including a stop member, the known position of the piston atwhich the locking devices can be moved to the locked position can be thedatum position.

Referring now to FIG. 2, another two-platen injection molding machine110 includes a base 112 and a first platen 114 and a second platen 116each mounted on the base 112. The first platen 114 is movable relativeto the second platen 116 between open and closed positions. In theexample illustrated, the second platen 116 is generally stationaryrelative to the base 112 during operation of the machine 110, and isalso referred herein as stationary platen 116. The first platen 114, inthe example illustrated, moves relative to the base 112 during operationof the machine 110 and is also referred herein as moving platen 114.

When in the closed position, the platens 114, 116 are drawn together.When in the open position, the platens 114, 116 are separated tofacilitate removal of a molded article from a mold formed at least inpart by first and second mold halves (mold portions) 114 a, 116 aaffixed to the platens 114, 116, respectively.

The machine 110 includes at least two tie bars 120 extending between thefirst and second platens 114, 116 for coupling the platens 114, 116together. In the example illustrated, four tie bars 120 are provided.Each of the four tie bars 120 are positioned generally at (and extendbetween) respective corners of the two platens 114, 116 (FIG. 3). Thetie bars 120 generally comprise elongate members aligned in parallelwith a machine axis 122 along which the moving platen 114 translates(each tie bar 120 having a tie bar axis 123 parallel to the machine axis122). The machine axis 122 passes through the center of a sprue bushing109 mounted in the stationary platen for receiving melt from aninjection nozzle 107.

A traverse actuator 124 can be coupled to the moving platen 116 to movethe platen 116 between the open and closed positions. In the exampleillustrated, the traverse actuator 124 comprises a single linearactuator in the form of a ball screw driven by a motor and in engagementwith a ball nut that is fixed, for example, to the moving platen 114.The tie bars 120 can define a tie bar envelope or space 199, and thetraverse actuator 124 can be positioned outside the space 199. In otherexamples, a belt drive system could be used as a linear actuator to movethe moving platen 114 between the open and closed positions. One or morerelatively long stroke, small diameter fluid cylinders could also beused as the traverse actuator.

Referring to FIGS. 4 and 5, the machine 110 further includes at leastone locking device 126 to selectively lock one of the platens 114, 116to one of the tie bars 120. In the example illustrated, a first one ofthe locking devices 126 (identified as first locking device 126 a) ismounted to the first platen 114 and associated with a first one of thetie bars 120 (identified as first tie bar 120 a). The first lockingdevice 126 a selectively secures the first platen 114 to, and releasesthe first platen 114 from, the first tie bar 120 a.

With reference also to FIG. 6, the first locking device 126 a cancomprise, for example, a lock nut element 128 of generally annularconstruction rotatably disposed in a housing 129 affixed to the movingplaten 114. In the example illustrated, the lock nut 128 is providedwith an inner bore with first teeth 130 arranged in axial rows, the rowsspaced circumferentially apart by first axial grooves 131. The first tiebar 120 a (having a first tie bar axis 123 a parallel to the machineaxis 122) can be provided with second teeth 132 that are similarlyarranged in axial rows, spaced apart circumferentially by second axialgrooves 133.

When in the locked position (as shown in FIG. 5), the first and secondteeth 130, 132 are oriented to be in circumferential registration witheach other, so that the first and second teeth inter-engage, therebyinhibiting relative axial motion between the first platen 114 and tiebar 120 a. The lock nut 128 can be rotated relative to the tie bar 120to an unlocked position (FIG. 6) in which the first teeth 130 arealigned with the second axial grooves 133 provided on the tie bar 120,and the second teeth 132 are aligned with the first axial grooves 131 ofthe lock nut 128, thereby allowing axial movement of the tie bar 120through the lock nut 128.

Before moving the locking device 128 from the unlocked to the lockedposition, the tie bar 120 can be moved axially relative to the lock nut128 to any one of a plurality of meshing positions in which the peaks ofone set of teeth are in axial registration with the valleys betweenadjacent ones of the other set of teeth. Adjacent meshing positions arespaced apart axially by an amount generally equal to the pitch of theteeth. Providing a plurality of meshing positions can facilitateaccommodating molds with different axial extents (different moldheights).

In one or more other examples, the locking device can comprise two halfnuts, each having first engagement elements to engage teeth on the tiebar 120 when in the locked position, and which can be moved away fromthe tie bar 120 generally perpendicular to the length thereof to beclear of the tie bar when in the unlocked position.

Referring to FIGS. 4 and 7, the machine 110 further includes at leastone clamping mechanism 136 mounted to one of the platens 114, 116 andassociated with one of the tie bars 120 for exerting a clamping force onthe platens 114, 116 during the injection mold cycle. In the exampleillustrated, the machine 110 includes a first clamping mechanism 136 amounted to the second platen 116 and associated with the first tie bar120 a. The first clamping mechanism 136 a can selectively exert a firstforce (clamping force) urging the first and second platens 114, 116together, and an optional second force (mold break force) urging thefirst and second platens 114, 116 apart. The first force (clampingforce) can have a magnitude of, for example, 80, 120, or 200 tons ormore, and generally defines a maximum rated load for the machine. Thesecond force can typically have a magnitude of about 5 percent to about10 percent of the first force (i.e. clamping force can be about 10 toabout 20 times or more greater than the mold break force).

The clamping mechanism 136 a includes a cylinder housing 138 affixed tothe second platen 116, and a piston 140 affixed to the first tie bar 120a and slidable within the cylinder housing 138. The language “affixedto” includes configurations in which the corresponding elements areseparately joined together, or are made of integral, one-piececonstruction. In some examples, the cylinder housing 138 may include aninsert or barrel separately attached to the platen. The piston 140 can,in some examples, be partially or entirely formed integrally with thetie bar.

With reference also to FIG. 8, in the example illustrated, the cylinderhousing 138 comprises a pocket 139 machined in the stationary platen116, the cylinder housing 138 being integral with the platen 116. Thepiston 140, in the example illustrated, comprises a piston head 142separately attached to the tie bar 120 a. The piston head 142 includesan axial bore 144 that has internal threads 146, for engagement withexternal threads 148 provided along an end portion of the tie bar 120 a.A keeper 149 can be positioned across the distal end face of the tie bar120 and bolted to the end face of the piston head 142 to facilitatelocking the piston head 142 in position relative to the tie bar 120.

The piston 140 further includes, in the example illustrated, a sealjournal 150 fitted with a piston seal 151 having a radially outersurface 152 in sealed engagement with an inner surface 154 of thecylinder housing 138. The cylinder housing 138 has a proximal end wall156 axially nearest the second mold half 116 a, and a distal end wall157 spaced axially apart from the proximal end wall 156. In the exampleillustrated, the distal end wall 157 comprises a cylinder cap 158 boltedto the platen 116 and having a bore 159 therethrough, an end portion ofthe piston 140 slidably received through the bore 159.

As seen in FIG. 7, the piston 140 and cylinder housing 138 cooperate toform a first chamber (also called a clamping chamber) 160 on one side(clamp side 161) of the seal journal 150, and a second chamber (alsocalled an unclamp chamber) 162 on a second side (unclamp side 163) ofthe seal journal 150 of the piston 140, axially opposite the first(clamp) side 161. Fluid can be fed into the clamp and unclamp chambers160, 162 via a clamping port 164 and unclamp port 166, respectively. Inthe example illustrated, the clamp and unclamp ports 164, 166 open to anexterior side of the cylinder housing 138.

In the example illustrated, the clamp side 161 and clamping chamber 160are disposed proximal the second mold half 116 a (relative to the sealjournal 150), and the unclamp side 163 and unclamp chamber 162 aredisposed axially distal the second mold half 116 a. Pressurizing theclamping chamber 160 can exert a force (axially in a clamp direction168) on a clamp face 170 of the piston 140, the clamp face 170 directedtoward the second mold half 116 a. Pressurizing the unclamp chamber 162can exert an axial force (in an unclamp direction 169) on an unclampface 172 of the piston, opposite the clamp face 170.

Each of the clamp and unclamp faces 170, 172 can comprise a single face,or a plurality of face sections spaced apart axially and/or radiallyalong the piston head 142. In the example illustrated, the clamp face170 includes a clamp end face portion 170 a (generally defined by thesurface area of the retaining ring 204 directed towards the proximal endwall 156—described further in relation to FIG. 8), and a clamp steppedface portion 170 b generally defined by the surface area of the annularorthogonal wall portion of the seal journal 150 facing towards theproximal end wall 156. The unclamp face 172 is, in the exampleillustrated, generally defined by the surface area of the annularorthogonal wall portion of the seal journal 150 facing away from theproximal end wall 156 (i.e. the face of the seal journal 150 directedtowards the unclamp side 163). The surface of the unclamp face 172 canbe stepped or notched at an outer radial edge thereof, for example, tofacilitate fluid flow into (or out of) the unclamp chamber 162 (via port166) even when the piston 140 is advanced to its maximum travel positionin the clamping direction (right-most position relative to the cylinderhousing 138).

The piston 140 is axially slidable within the cylinder housing among aclamping position 176 (FIG. 9), an unclamped position 178 (FIG. 10), anda datum position 180 (FIG. 11). The maximum axial spacing between theclamping position 176 and the unclamped position 178 can generally bedefined by axially opposed end walls (e.g. end walls 156, 157), and/orradially inwardly protruding step walls (e.g. step wall 206), betweenwhich the piston 140 is confined to travel. The datum position 180 is,in the example illustrated, located axially intermediate the clampingand unclamped positions 176, 178.

The piston 140 can be moved to, and selectively released from, the datumposition 180. In the example illustrated, the locking device 126 can bemoved from the unlocked to the locked position when the piston 140 is inthe datum position (i.e. axial position of the tie bar and its teethrelative to the stationary platen and its teeth can be accuratelycomputed via the machine coordinate system). In some examples, the datumposition 180 can define the position of the piston 140 at which clampingtogether of the platens 114, 116 is initiated (i.e. delivery ofpressurized fluid to the clamping chamber 160 for generating the clampforce is initiated when the piston 140 is in the datum position 180).Initiating clamp-up at an axially intermediate position (i.e. at thedatum position 180) can ensure that sufficient axial piston travel isavailable in both the clamp direction 168 (to apply the required clampforce), and in the unclamp direction 169 (to effect separation of themold halves 114 a, 116 a after an injection cycle). Sufficient travel inthe unclamp direction 169 can be particularly advantageous in caseswhere the machine 110 is set up such that minimal axial displacement ofthe moving platen 114 occurs during clamp-up, and/or in cases of moldflash during the injection cycle.

The datum position 180 can be defined by a mechanical stop memberconfigured to inter-engage with the piston 140 and the cylinder housing138 when the piston 140 is in the datum position 180. In the exampleillustrated, the clamping mechanism 136 includes (as an example of astop member) a positioning member 182 moveable between advanced andretracted positions 192, 194. The positioning member 182 is moveablerelative to the piston 140 and relative to the cylinder housing 138, andcan be selectively retained in, and released from, the advanced position194.

In the example illustrated, the positioning member 182 comprises anannular body or sleeve 190 (FIG. 8) slidably coupled to the piston 140,and coaxial therewith. The positioning member 182 is axiallydisplaceable relative to the piston 140 between the advanced andretracted positions 192, 194. The positioning member comprises aproximal end face 196 having a radially inner portion defining a firstcontact surface 198, and a radially outer portion defining a secondcontact surface 200. The contact surfaces 198, 200 cooperate with otherelements to provide a positive mechanical stop for the positioningmember 182. In the example illustrated, the first and second contactsurfaces 198, 200 are generally coplanar, and are disposed adjacent anaxial end (proximal end 196) of the positioning member nearest thesecond mold half 116 a.

The piston 140 has a first abutment surface 202 for engagement with thefirst contact surface 198 of the positioning member 182 when thepositioning member 182 is in the advanced position 194. The firstabutment surface 202 is fixed to, and moves with, the piston 140 duringoperation of the machine 110. In the example illustrated, the firstabutment surface 202 comprises a radially outwardly protruding shoulderportion of a retaining ring 204 mounted to the proximal end of thepiston head 142. The first abutment surface 202 is spaced apart from theseal journal 150 on the clamping side 161 of the piston 140. Thepositioning member 182 can generally move axially between the firstabutment surface 202 and the seal journal 150. Displacement of thepositioning member 182 towards the seal journal 150 generallycorresponds to the retracted position 194 of the positioning member 182relative to the piston 140. In the example illustrated, the positioningmember 182 is disposed on the clamp side 161 of the seal journal 150 ofthe piston 140.

A second abutment surface 206 is affixed to the cylinder housing 138 forengagement with the second contact surface 200 of the positioning member182 when the piston 140 is in the datum position 180 and the positioningmember 182 is in the advanced position 194. The second abutment surface206 is in an axially fixed position relative to the stationary platen116 during operation of the machine 110. In the example illustrated, thesecond abutment surface 206 comprises an annular radially inwardlyprotruding step 208 extending from the inner surface 154 of the cylinderhousing 138.

A pushing member 211 can be provided for exerting a positioning force onthe positioning member 182 to move and/or releasably retain thepositioning member 182 to/in the advanced position. In the exampleillustrated, the pushing member 211 comprises a positioning fluidchamber 212. The positioning force is generated by pressurizing thepositioning fluid chamber 212 which is adjacent to, and in fluid contactwith, a distal end face 214 of the positioning member 182. The distalend face 214 of the positioning member is generally defined by aradially extending end wall of the annular body 192, disposed axiallyopposite the proximal end face 196. Fluid can be supplied to orevacuated from the positioning fluid chamber 212 via a positioning port216, which, in the example illustrated, extends radially through thecylinder housing 138, at a position axially between the clamping port164 and the unclamp port 166. The distal end face 214 can be stepped ornotched at its radially outer edge to help ensure satisfactory fluidcommunication between the positioning fluid chamber 212 and thepositioning port 216, even when the positioning member 182 is at itsmaximum rightward travel position relative to the positioning port 212(i.e. when the positioning member is in the fully retracted position 194and the piston 140 is in the clamp position 176).

In the example illustrated, the positioning fluid chamber 212 isdisposed (axially) on the clamping side 161 of the piston 140 (i.e. onthe clamping side 161 of the seal journal 150), between the positioningmember 182 and the seal journal 150 of the piston 140. The positioningchamber 212 extends radially between an outer surface of the piston 140and the inner surface 154 of the housing 138 (FIG. 7). One end (i.e.proximal axial end) of the positioning chamber 212 is, in the exampleillustrated, sealed by the seal journal 150 (with seal 151). Theopposite end (distal axial end) can be sealed by radially inner andouter positioning member seals 218 a, 218 b, respectively. The radiallyinner positioning member seal 218 a can be disposed between the innersurface of the positioning member 182 and an outer surface of the piston140. The radially outer positioning member seal 218 b can be disposedbetween an outer surface of the positioning member 182 and the innersurface 154 of the cylinder housing 138.

In use, an example is considered where new mold halves 114 a, 116 a areinstalled on the platens 114, 116, and wherein the shut-height of thenew mold is not known. Once the mold halves have been attached to theplatens, and with the locking devices 126 in the unlocked position, thetraverse actuator 124 can be energized to jog the moving platen 114(e.g. in set-up mode) towards the stationary platen 116 until the moldis closed (mold halves 114 a, 116 a just or nearly touch).

Prior to completing the step of closing the mold, the clampingmechanisms 136 (and pistons 140 thereof) can be moved to the datumposition 180, by pressurizing the positioning fluid chamber 212 and theunclamp chamber 162 with, for example, hydraulic fluid, and opening theclamping port 164 to tank to evacuate fluid from the clamp chamber 160.The positioning force exerted by the pressurized positioning fluidchamber 212 urges the positioning member 182 left (in the unclampdirection 169 in FIG. 10) relative to the piston 140 (in other words,urges the piston 140 right relative to the positioning member 182), sothat the first contact surface 198 bears against the first abutmentsurface 202 (FIG. 11). The pressure in the unclamp chamber 162 exerts adatum force on the piston, urging the piston 140 (with the positioningmember 182 coupled thereto) towards the left in FIG. 11, so that thesecond contact surface 200 engages the second abutment surface 206. Thedatum force on the piston 140 urging the piston left relative to thepositioning member 182 (so as to urge the positioning member towards theretracted position) is less than the positioning force urging the pistonright relative to the positioning member (urging the positioning memberto the advanced position), so the positioning member 182 remains in theadvanced position 192 relative to the piston 140 and the piston isretained in the datum position 180 (in the position as shown in FIG.11).

To provide a datum force (exerted by the pressurized unclamp chamber162) that is less than the positioning force (exerted by the pressurizedpositioning fluid chamber 212), the pressure of the fluid can be lowerin the unclamp chamber 162 than in the positioning fluid chamber 212.Alternatively or additionally, the effective relative surface areasagainst which the fluid in the respective chambers 162, 212 bears can beconfigured to ensure the desired differential in axial forces isachieved. In the example illustrated, the surface area of the unclampface 172 of the piston (having a radial extent 219) is less than thesurface area of the distal face 214 of the positioning member 182(having a radial extent 221, which subsumes and extends beyond theradial extent 219). Having differently sized surface areas of the faceson which pressurized fluid in the chambers 212, 162 act can provide thedesired difference in force magnitudes while having equal fluid pressurein the chambers 212, 162, which can reduce the number of pressurecontrol valves (or similar) required in the machine 110.

The machine 110 can include a controller in communication with anencoder, linear transducer, or the like for accurately reading the axialposition of the moving platen 114 relative to a machine coordinatesystem, and so the position of the moving platen 114 corresponding tothe mold closed position can be recorded in the machine controller. Whenthe piston 140 is in the datum position 180, the precise axial positionof the tie bar 120 (and its teeth 132) relative to the stationary platen116 (and hence relative to the machine coordinate system) is known. Thiscan facilitate accurate movement of the platen 114 (with lock nut 128)to a meshing position relative to the tie bar 120.

The recorded “mold closed” position of the moving platen 114 can becompared to the nearest previous meshing position for the locking device126 (i.e. relative axial position in which the peaks of one set of teethare axially aligned with the valleys of the other set of teeth). Themoving platen 114 can then be moved back (in the unclamp direction) tothat nearest meshing position (by an axial distance defined as an offsetamount), and this new position of the moving platen can be recorded inthe controller as the “rapid advance” position for future injectioncycles with the given mold halves 114 a, 116 a. In other words, theaxial position of the rapid advance position to which the moving platenis shuttled by the traverse actuator corresponds to a meshing position(position of the moving platen 114 relative to tie bar 120 in which thelocking device 126 can be moved to the locked position) and to a nearmold closed position (or mold closed position if offset is about zero)position of moving platen 114 relative to stationary platen 116 in which

The offset amount need generally not be more than the pitch of teeth ofthe locking device 126, and can range, for example, from near or equal 0mm to about 4 mm or about 12 mm. The magnitude of the offset amount canbe minimized (and can in some cases be reduced to about zero) byloosening the keepers 149 and rotating the piston head 142 relative tothe tie bars 120 to adjust the relative axial position of the tie bar120 (and its teeth 132) when the piston 140 is in the datum position.This can adjust the axial position of the meshing positions with respectto the stationary platen 116.

Once the offset and the rapid advance positions have been established,the machine can be returned to a home state (locking devices unlocked,mold fully opened). Normal run mode can then be initiated.

In run mode, the traverse actuator 124 can shuttle the moving platen 114to the rapid advance position (i.e, towards the closed position).Generally prior to completing this shuttling step, the pistons 140 ofthe clamping mechanisms 136 can each be moved to the datum position, sothat the tie bars 120 are in a meshing position when the traverseactuator 124 completes shuttling the moving platen to the rapid advanceposition. The locking devices 126 can then be moved to the lockedposition.

With the moving platen 116 locked to the tie bars 120, and the piston140 already in the datum position 180 (from the previous step), themachine 110 is ready for the clamp force to be applied (FIG. 11). Foreach of the clamping mechanisms 136, pressurized fluid can be fed intothe clamping chamber 160 (via clamping port 164), and the unclamp port166 can be opened to tank, relieving any pressure in the unclamp chamber162 (FIG. 9). In the example illustrated, the clamp force exerted by thepressurized fluid in the clamp chamber 160 is greater then the unclamp(mold break) force, and can be from about 10 times to about 20 times (ora higher factor) greater than the unclamp force. The effective surfacearea of the face on which the pressure in the clamp chamber 160 acts(i.e. directly acting on surfaces 170 a and 196 as seen in FIG. 7) canbe greater than the surface area of the unclamp face 172 by acorresponding proportional amount. The clamp chamber 160 can bepressurized (during clamp up) with fluid at the same pressure as thatprovided to the unclamp chamber 162 (during mold break, where a moldbreak force is desired), and the desired difference in force magnitudecan be provided as a result of the difference in effective surface areason which the pressurized fluid acts.

During clamping together of the mold halves 114 a, 116 a, thepositioning chamber 212 can be, but need not be, maintained in apressurized state. Maintaining pressurized fluid in the positioningchamber 212 can reduce the oil consumption required for filling theclamping chamber 160 upon clamp-up, by keeping the positioning member182 in or near the advanced position 192 and so reducing the volume ofthe clamping chamber 160 to be filled upon clamp-up. In the exampleillustrated, the effective surface areas of the axially opposite facesof the positioning member exposed to the clamping chamber 160 and thepositioning chamber 212 are about equal (i.e. the effective surface areof distal end face 196 is generally equal to the effective surface areaof proximal end face 214. During mold clamping, fluid at about the samepressure setting is fed into each of the clamping chamber 160 and thepositioning chamber 212. The positioning member 182 is in the advancedposition when clamping is initiated, and remains in that position sincethe left and right axial forces acting on the respective end faces aregenerally balanced. The force exerted by the pressure of the fluid inthe clamping chamber 160 is transmitted through the positioning member182 and through the pressurized fluid in the positioning chamber 212,and ultimately against the clamp side 161 of the seal journal (face 170b) (FIG. 9).

Once the piston 140 has moved to the clamping position (to the right asshown, for example, in FIG. 9) and the desired clamping pressure isachieved, the melt can be injected into the mold halves 114 a, 116 a.

Upon completion of injection and after waiting a period of time as maybe required for sufficient solidification of the molded articles, clamppressure can be released (opening the clamp valve 164 to tank). Where amold break force is optionally provided, the unclamp force can beapplied by the clamping mechanisms 136 (pressurizing the unclamp chamber162 via the unclamp port 166). The positioning chamber 212 can bedepressurized (opening port 216 to tank), so that as the piston moves inthe unclamp direction 169 (to the left in FIG. 9), the piston can movepast the datum position without interference with the positioning member182 that would otherwise stop the piston in the datum position (i.e.positioning member 182 can move towards the retracted position 194; seeFIG. 10). Accordingly, even with minimal forward travel of the piston140 for clamp-up, or in cases of mold flash, sufficient travel of thepiston (and hence the moving platen 114) in the unclamp direction 169 isavailable by urging the piston axially (in the unclamp direction) pastthe datum position.

After the pressure in the clamp chamber has been relieved (and after thepiston has been moved to the unclamp position in cases where a moldbreak force is optionally provided), the locking device(s) 126 (whichare still in the locked position but are under no load since axialforces on the tie bar 120 have been relieved) can be moved to theunlocked position. The traverse actuator 124 can then be energized toshuttle the moving platen 114 back to an open position, away from thestationary platen 116. The molded articles can be ejected from the moldhalves 114 a, 116 a, and the next cycle can commence. In some examples,the piston 140 can be moved back to the datum position while thetraverse actuator shuttles the moving platen 114 to the open position,and/or during ejection of the molded articles. Moving (or at leastpartially moving) the piston to the datum position during one or both ofthe advance and return strokes of the traverse actuator 124 can savecycle time.

Further details of other aspects of the machine 110 will now bedescribed. With reference again to FIG. 5, in the example illustrated,the locking device comprises a lock housing 129 having an inner surfaceaffixed to the moving platen 114 and extending coaxially with the tiebar axis 123 a. In the example illustrated, the housing 129 is integralwith the platen 114 and comprises a bore provided in the platen. Theinner surface of the housing 129 can be stepped, providing a firstbearing face 222 and a second bearing face 224 each extending generallyradially inwardly of the housing 129 at spaced apart locations along theaxis of the housing. In the example illustrated, the first and secondbearing faces 222, 224 are spaced axially apart by a first housingspacing 226. The first bearing face 222 is, in the example illustrated,positioned axially away from (or distal) the stationary platen 116. Thesecond bearing face 224 is axially nearest (or proximal) the stationaryplaten 116.

The lock nut 128 of the locking device 126 is received within thehousing 129 and rotatable within the housing about the axis 123 abetween the locked and unlocked positions. The lock nut 128 has agenerally annular body with axially opposite first and second ends 227,229. The first end (distal end) 227 is directed away from the stationaryplaten 116, and the second end (proximal end) 229 is directed towardsthe stationary platen 116. An inner bore 230 extends coaxially throughthe nut 128 from the first end to the second end, for receiving the tiebar 120 therethrough. The inner bore 230 defines a radially innersurface having radially inwardly projecting elements (i.e. first teeth130 in the example illustrated) extending therefrom. The projectingelements 130 engage the tie bar 120 when the lock nut 128 is in thelocked position, to transfer the axial clamp load (and unclamp load)from the tie bar 120 to the lock nut 128.

The body of the lock nut 128 has a radially outer surface 232 oppositethe inner surface, the outer surface 232 including first and second stepfaces 234, 236 for abutting the first and second bearing faces 222, 224,respectively, to cooperatively transfer the axial clamp load from thelock nut 128 to the platen 114. The bearing faces 222, 224 are, in theexample illustrated, generally planar surfaces oriented generallyperpendicular to the axis 123.

In the example illustrated, the first (distal) step face 234 abuts thefirst bearing surface 222 generally continuously during operation of themachine 110. The surfaces 234, 222 are in flush engagement whether ornot a clamp load is being applied across the platens 114, 116. Anannular retaining plate 238 can be mounted to the platen 114 forengaging the nut 128 and holding the first step face 234 against thefirst bearing surface 222. The retaining plate 238 can have a radiallyinwardly protruding wall 239 that bears against a shoulder surface 240protruding radially outwardly from the nut 128, at an axial positionspaced rearward (distally) of the first step face 234. The contactbetween the surfaces 222, 234 can serve a locating function, providing aknown position of the teeth 130 relative to the moving platen 114 (andhence to the machine coordinate system), at least when the tie bars 120and lock nut 128 are unloaded (i.e. in relaxed, untensioned state).Engagement between the faces 239 and 240 can also be used, in theillustrated example, to transfer an unclamp force from the nut 128 tothe platen 114.

The second step face 236 can be spaced apart from the second bearingsurface 224 when the lock nut 128 is unloaded (for example by a firststretch gap 242), and the second step face 236 can abut the secondbearing surface 224 when the axial clamp load is applied to the nut 128.In the example illustrated, the second step face 236 is axially spacedapart from the first step face 234 by a first (proximal) nut spacing244. The proximal nut spacing 244 is less than the first housing spacing226 when the nut 128 is unloaded, the difference between the firsthousing spacing 226 and the first nut spacing 244 being equal to thefirst stretch gap 242.

The lock housing 129 can be provided with additional axial load bearingsurfaces, such as, for example, a third (intermediate) bearing surface246 positioned axially intermediate the first and second bearingsurfaces 222, 224. The third bearing surface 246 is, in the exampleillustrated, oriented generally perpendicular to the axis 123, and isspaced apart from the first bearing surface 222 by an intermediatehousing spacing 248. The lock nut 128 can include a third step face 250axially intermediate the first and second step faces 234, 236, and inadjacent facing relation to the third bearing surface 246 forcooperating with the first and second step faces 234, 236 to transferthe axial clamp load from the nut 128 to the platen 114.

In the example illustrated, the third step face 250 is spaced axiallyapart from the third bearing surface 246 (for example by an intermediatestretch gap 252) when the nut 128 is unloaded, and the third step face250 abuts the third bearing surface 246 when the axial clamp load isapplied to the nut 128. In the example illustrated, the intermediatestep face 250 is axially spaced apart from the first step face 234 by asecond (intermediate) nut spacing 254. The intermediate nut spacing 254is less than the intermediate housing spacing 248 when the nut 128 isunloaded, the difference between the intermediate housing spacing 248and the intermediate nut spacing 254 being equal to the intermediatestretch gap 252.

The intermediate stretch gap 252 is, in the example illustrated, lessthan the proximal stretch gap 242. In use, upon initial application ofpressurized fluid in the clamping chamber, the tie bar 120 is urgedtowards the right (in FIG. 5), urging the lock nut 128 (throughinter-engagement of the teeth 130, 132) also towards the right. Some ofthe clamp load is immediately transferred to the platen 114 from the nut128 through the abutment of the first step face 234 against the firstbearing surface 222. As the clamp load increases, the tie bar stretches,resulting in maximum rightward displacement of the right-most end of thetie bar, and zero displacement at the left-most end of the tie bar 120.Along the axial extent of the tie bar 120 that is within the bore of thelock nut 128, the same is true (more axial displacement of the tie barat the right or proximal end than at the left or distal end). Theproximal and intermediate stretch gaps can allow the lock nut 128 tostretch axially with the tie bar, so that once full clamping pressure isreached, the load is distributed across the bearing surfaces 222, 246,and 224. The loading on the teeth 130, 132 can also be uniformlydistributed across the axial extent of the lock nut 128 by accommodatingtie bar stretch through the provision of the plural bearing surfaces222, 224, 246 and the stretch gaps 242, 252.

Without provision for stretch gaps as disclosed above, the stepped locknut 128 can still provide enhanced force distribution across the axialextent of the nut and the engaged teeth 130, 132. However, with theprovision of the stretch gaps, the lock nut can stretch with the tiebar, and the stress on the tie bar and lock nut can be distributed morebroadly and more uniformly. Without the steps and/or without the stretchgaps, the stress would generally be more concentrated in a localizedaxial position, typically near the front (proximal) end of the nut. Morelocalized, concentrated stress loading can reduce the overall machineclamp capacity and/or reduce the service life of the locking devicecomponents, including the tie bar in some cases.

A generally sealed lubrication chamber 260 can be provided between atleast a substantial portion of the radially outer surface of the lockingnut 128 and the inner surface of the housing 129. Lubrication fluid canbe provided in the lubrication chamber 260 to further facilitaterotation of the locking nut 128 between the locked and unlockedpositions. A proximal seal 262 (e.g. a radial shaft seal) can beprovided between the outer surface of the nut 128 and the housing 129 ata proximal end of the nut to seal off the proximal end of the chamber260. A distal seal 264 can be provided at the distal end of the lockingnut 128 to seal off the chamber 260 at the distal end. The distal seal264, in the example illustrated, comprises a radially outer seal 266(mounted between the housing 129 and the retainer 238) and a radiallyinner seal 268 (mounted between the nut 128 and the retainer 238). Avalved fill port 270 can extend between the two seals 266, 268 forfilling the chamber 260. A drain port 271 can similarly be provided, ata lower point around the circumference of the chamber 260.

In the example illustrated, the lubrication fluid can be unpressurized,i.e. maintained at generally atmospheric pressure, since the lockingdevice 126 is free of (or isolated from) any pressure chambers forgenerating a clamping force or an unclamp force. This can reduce thepressure rating requirements for the seals 262, 264 which can permit useof lower friction seals, which in turn can further reduce the time andenergy required to move the locking device 126 between the locked andunlocked positions.

Referring again to FIG. 2, the traverse actuator 124 can be free ofprovisions for providing an unclamp force (or mold break force) after aninjection cycle. Such provisions can be understood with reference to aprior art injection molding machine, wherein the traverse actuator(s)provide an unclamp force of at least about 5% to 10% of the clamp force,and the traverse actuator(s) are arranged so that this force isgenerally equally balanced about the vertical and horizontal centerpoint of the platen (e.g. a single actuator located generally centrallyof the mold, or plural actuators arranged symmetrically about the centerpoint). Even for dedicated machines running a process in which a moldbreak force is not normally required, the machine can advantageously beequipped with provision for applying a mold break force in case the molddoes not open as expected (e.g. as may be caused, for example, by moldflash).

In the example illustrated, the clamp mechanism 136 of the injectionmolding machine 110 provides the capability to apply an unclamp (moldbreak) force to separate the platens 114, 116 after an injection cycle,if necessary. The traverse actuator 124 of the injection molding machine110 can be sized with a significantly lower maximum force rating thanwould otherwise be required if it were relied upon to provide theunclamp (mold break) force. In the example illustrated, the maximumforce rating of the traverse actuator 124 in the mold open direction isabout 3% of the maximum clamp force of the machine. In other examples,the traverse actuator 124 may be only 1% (or less) of the maximum clampforce of the machine 110. Furthermore, the traverse actuator 124 mayalternatively or additionally be arranged to exert its opening andclosing force at a point that is laterally offset with respect to thecenter 115 of the moving platen 114. Further details of the traverseactuator 124 are described subsequently herein.

Referring to FIG. 12, an alternative example of a clamping mechanism 336is shown. The clamping mechanism 336 is similar to the clampingmechanism 136, with like features identified by like referencecharacters, incremented by 200.

The clamping mechanism 336 comprises a pushing member 411 for exerting apositioning force on the positioning member 382 to move and/orreleasably retain the positioning member 382 to/in the advancedposition. In the example illustrated, the positioning force is generatedby springs 511 acting between the distal end face 414 of the positioningmember 382 and the piston 140, urging the positioning member away fromthe clamping side 361 of the seal journal 350.

In use, the piston 340 is moved to the datum position by relievingpressure in the clamp chamber 360 (e.g. venting port 364 to tank in theexample illustrated). The springs 511 can move the positioning member tothe advanced position relative to the piston (i.e. with the firstcontact surface 398 bearing against the first abutment surface 402 ofthe retainer 404. The unclamp chamber 362 is pressurized so that itexerts a datum force on the piston 340 that is less than the positioningforce exerted by the springs 511. Accordingly, the positioning member382 is retained in the advanced position relative to the piston by thesprings 511. The pressure of the clamp chamber moves the piston intoposition so that the second (radially outer) contact surface 400 of thepositioning member 382 remains engaged with the second abutment surface406 of the cylinder housing.

During clamping of the platens, the unclamp chamber can bedepressurized, and the clamp chamber pressurized. The pressure in theclamp chamber exerts a force on the piston to move the piston towardsthe clamped position. The springs may or may not compress during theclamping of the platens. Pressurized fluid in the clamping chamber canbear directly against the end face of the piston and/or the clampingshoulder of the piston (face 370 b). Fluid may flow around or throughthe positioning member (e.g. through apertures in the positioningmember) to access the clamping shoulder from the clamping port 364. Forcertain applications, particular for long running, low-cycle timeapplications, the machine can be set up so that the total axial travelof the piston from the datum position to full clamping of the platenscan be minimized, and can be as short as a few millimeters or less.

During unclamp (mold break), the clamping chamber 360 can bedepressurized (port 364 vented to tank), and the unclamp chamber 362pressurized (high pressure fluid fed through port 366). The axial forcegenerated by the pressurized unclamp chamber 362 can be greater than theforce exerted by the springs 511, so that the springs can compress,allowing the positioning member 382 to be displaced towards theretracted position relative to the piston 340. The ability of the piston340 to move in an unclamp direction (i.e. left in FIG. 12) past itsaxial position upon initiating clamp-up (i.e. past the datum position)can help to ensure that sufficient unclamp stroke length is available toseparate and relieve the pressure on the clamped mold halves 314 a, 316a. This unclamp stroke length is available even in cases where thepiston travel from datum to fully clamped platens is minimal, and/or incases where the mold has flashed.

Considering again the traverse actuator 124, and with reference now toFIGS. 13 and 14, traverse actuator 124 of the machine 110 can take theform of a single linear actuator 124 a mounted at or near the lower end117 of the moving platen 114. In the example illustrated, the singlelinear actuator 124 a comprises a motor 113 coupled to a ball screw 119.The motor 113 may be a hollow motor attached to (and moveable with) themoving platen 114, with a ball nut 121 rotatably housed within the motor113.

The single linear actuator 124 a of the traverse actuator 124 extendsalong an actuator axis 105 that is generally parallel to the machineaxis 122 and offset in at least one of a horizontal and verticaldirection from the machine axis 122. In the example illustrated, theactuator axis 105 is vertically offset from the geometrical center ofthe platens 114, 116 (i.e. spaced vertically beneath the axis 122 by anactuator offset 103). The single actuator 124 a applies a net openingforce on the moving platen that acts along the actuator axis 105 in adirection opposite the clamping force. In some examples, the singleactuator 124 a can additionally or alternatively be positionedhorizontally offset from the axis 122. The offset configuration of thesingle actuator 124 a can provide additional space and flexibility withrespect to overall packaging of components in the injection moldingmachine 110.

Referring to FIG. 15, another example of a traverse actuator 1524configuration for an injection molding machine 1510 is illustrated,having features similar to that of the machine 110 identified with likereference numerals, incremented by 1400. The traverse actuator 1524 isalso free of provision for providing an unclamp force after an injectioncycle, and the traverse actuator 1524 is arranged to exert its openingand closing force at a point that is laterally offset with respect tothe center 1515 of the moving platen 1514. In the example illustrated,the traverse actuator 1524 comprises a first ball screw 1519 a and asecond ball screw 1519 b mounted at or near the lower end 1517 of themoving platen 1514, on horizontally opposed sides of the moving platen1514 (i.e. on either side of the axis 1522). First and second motors1513 a, 1513 b are coupled to the respective ball screws 1519 a, 1519 b.The motors 1513 are, in the example illustrated, fixed to the machine1510 at or near a lower surface of the stationary platen 1516.Respective ball nuts 1521 a, 1521 b are fixed to a lower surface of themoving platen 1514, to receive the respective ball screws 1519 a, 1519 btherethrough. In this configuration, each ball screw 1519 extendsbetween the fixed and moving platens 1514, 1516, parallel to the tiebars 1520. Each ball screw 119 has a proximal end 101 that is axiallypositioned at about the same axial position as the stationary platen,and an opposing distal end is directed towards the moving platen. Thisconfiguration can reduce outward axial extension of the traverseactuator 1524 (i.e. in a direction extending from one platen away fromthe other platen), which can further facilitate packaging of machinecomponents and minimizing overall axial length of the machine 1510.

Referring to FIG. 16, another example of a traverse actuator 1624configuration for an injection molding machine 1610 is illustrated,having features similar to that of the machine 1610 identified with likereference numerals, incremented by 1500. The traverse actuator 1624 isalso free of provisions for providing an unclamp force after aninjection cycle, and the traverse actuator 1624 is arranged to exert itsopening and closing force at a point that is laterally offset withrespect to the center 1615 of the moving platen 1614. In the exampleillustrated, the traverse actuator 124 includes a motor 1613 mounted tothe machine base at a position generally beneath the moving platen whenthe moving platen is in the retracted (mold open) position. The motor1613 rotates a pair of drive pulleys 1635 via a shaft 1637, all of whichare mounted to the machine base. A pair of spaced apart idler pulleys1641 are secured to the stationary platen, and a respective toothed belt1643 extends between respective ones of the drive pulleys 1635 and idlerpulleys 1641. The moving platen is secured to the belts 1635 via beltcoupling plates 1645 mounted to an underside surface of the movingplaten 1614.

While the above description provides examples of one or more processesor apparatuses, it will be appreciated that other processes orapparatuses may be within the scope of the accompanying claims.

1. An injection molding machine, comprising: a) a first platen and asecond platen, the first platen movable relative to the second platen inan axial direction between open and closed positions; b) a plurality oftie bars extending generally between the first and second platens forcoupling together the first and second platens; c) at least a firstlocking device mounted to the first platen and associated with a firstone of the tie bars, the first locking device and first tie barcomprising respective locking elements moveable from an unlockedposition to a locked position when the tie bar is moved axially relativeto the locking device to one of a plurality of axially spaced apartmeshing positions, the first locking device locking together the firsttie bar and the first platen when in the locked position, and the firstlocking device moveable from the locked position to the unlockedposition to release the first platen from the first tie bar; and d) atleast a first clamping mechanism mounted to the second platen andassociated with the first tie bar, the first clamping mechanismcomprising a piston member affixed to the first tie bar and movablebetween clamp and unclamp positions within a cylinder housing affixed tothe second platen, the piston and cylinder housing defining a clampchamber and an unclamp chamber on opposite sides of the piston, formoving the piston towards the clamp and unclamp positions and exerting aclamping force and a mold break force, respectively, when pressurized,the clamping force being less than or equal to a maximum rated loadassociated with the machine; and e) a traverse actuator comprising oneor more linear actuators coupled to at least one of the first and secondplatens for effecting said movement of the first platen relative to thesecond platen between the open and closed positions, the one or morelinear actuators together being free of provision for applying a moldbreak force to the platens.
 2. The injection molding machine of claim 1,wherein the one or more linear actuators of the traverse actuatortogether apply a net axial opening force on the at least one platen in adirection opposite the clamping force and at a vertical and/orhorizontal location that is substantially offset from the center of theat least one platen as viewed in a plane orthogonal to the axialdirection.
 3. The injection molding machine of claim 2, wherein the oneor more linear actuators of the traverse actuator together are sized toexert a maximum opening force on the at least one platen in a directionopposite the clamping force that is less than about 3 percent of themaximum rated load.
 4. The injection molding machine of any one ofclaims 1-3, further comprising a stop member movable relative to thepiston and the cylinder housing and moveable between an advancedposition and a retracted position, the stop member when in the advancedposition providing a mechanical stop for the piston when the piston ismoved to a datum position intermediate the clamp and unclamp positions.5. The injection molding machine of claim 2, wherein the traverseactuator comprises a motor, and the motor is mounted beneath at leastone of the first platen and the second platen.
 6. The injection moldingmachine of claim 2, wherein the traverse actuator comprises a motor, andthe motor is positioned at an axial position generally equal to that ofone of the first platen and the second platen.
 7. The injection moldingmachine of claim 2, wherein the traverse actuator comprises a motor, andthe motor is axially inboard of one of the first platen and the secondplaten.
 8. The injection molding machine of any one of claims 1-7,wherein the traverse actuator comprises a ball screw coupled to themotor and a ball nut fixed to the other of the first and second platensand in engagement with the ball screw.
 9. The injection molding machineof any one of claims 1-7, wherein the traverse actuator comprises atoothed belt driven by the motor and affixed to the other of the firstand second platens.
 10. The injection molding machine of any one ofclaims 1-9, wherein the injection molding machine comprises four tiebars extending between respective corners of the first and secondplatens, and wherein the traverse actuator is positioned outside of aspace bounded by the tie bars.
 11. The injection molding machine of anyone of claims 1-10, wherein one of the first and second platens is astationary platen remaining in a fixed axial position during use, andwherein the single linear actuator has a proximate end axiallypositioned generally at the fixed axial position of the stationaryplaten.
 12. An injection molding machine, comprising: a) a first platenand a second platen, the first platen movable relative to the secondplaten in an axial direction between open and closed positions; b) asprue bushing mounted in one of the first and second platens generallyat a geometrically central position thereof, the sprue bushing receivingmelt from an injection nozzle therethrough, the machine having a machineaxis parallel to the axial direction and passing through the spruebushing; c) a plurality of tie bars extending generally between thefirst and second platens for coupling together the first and secondplatens; d) at least a first locking device mounted to the first platenand associated with a first one of the tie bars, the first lockingdevice and first tie bar comprising respective locking elements moveablefrom an unlocked position to a locked position when the tie bar is movedaxially relative to the locking device to one of a plurality of axiallyspaced apart meshing positions, the first locking device lockingtogether the first tie bar and the first platen when in the lockedposition, and the first locking device moveable from the locked positionto the unlocked position to release the first platen from the first tiebar; e) at least a first clamping mechanism mounted to the second platenand associated with the first tie bar, the first clamping mechanismcomprising a piston member affixed to the first tie bar and movablebetween clamp and unclamp positions within a cylinder housing affixed tothe second platen, the piston and cylinder housing defining a clampchamber and an unclamp chamber on opposite sides of the piston, formoving the piston towards the clamp and unclamp positions and exerting aclamping force and a mold break force, respectively, when pressurized,the clamping force being less than or equal to a maximum rated loadassociated with the machine; and f) a traverse actuator comprising asingle linear actuator coupled to at least one of the first and secondplatens for effecting said movement of the first platen relative to thesecond platen between the open and closed positions, wherein the singlelinear actuator of the traverse actuator extends along an actuator axisthat is generally parallel to the machine axis and offset in at leastone of a horizontal and vertical direction from the machine axis. 13.The injection molding machine of claim 12, wherein the single linearactuator is sized to exert a maximum opening force on the at least oneplaten in a direction opposite the clamping force that is less thanabout 3 percent of the maximum rated load.
 14. The injection moldingmachine of claim 12, wherein the injection molding machine comprisesfour tie bars extending between respective corners of the first andsecond platens, and wherein the single linear actuator is positionedoutside of a space bounded by the tie bars.
 15. The injection moldingmachine of any one of claim 12, wherein one of the first and secondplatens is a stationary platen remaining in a fixed axial positionduring use, and wherein the single linear actuator has a proximate endaxially positioned generally at the fixed axial position of thestationary platen.
 16. The injection molding machine of any one of claim12, wherein the traverse actuator comprises a motor coupled to thesingle linear actuator, and the motor is mounted beneath at least one ofthe first platen and the second platen.
 17. The injection moldingmachine of any one of claim 12, wherein the traverse actuator comprisesa motor coupled to the single linear actuator, and the motor ispositioned axially between, and laterally aside, the first platen andthe second platen.